THIS INVENTION relates to a chemical agent for improving the engineering properties of soil.
In many civil engineering situations it is essential that the in situ soil have its engineering properties improved before being used in construction works. This is particularly important in road building where failure properly to stabilize the underlying soil can result in the road subsiding and/or cracking in use.
The simplest way of improving soil properties is by compacting it. However, because soils vary from sandy material through to clayey material, simply compacting the soil does not necessarily improve its engineering properties sufficiently to support whatever is constructed upon it. As a result of this it has been proposed to incorporate chemical agents into the soil to improve it and many stabilizers based on polymers have been used. These are successful in improving the soil""s properties but only for a relatively short period of time. Eventually the polymer leaches out of the soil and its effect is lost.
Whilst the chemical agent of the present invention is intended specifically to stabilize an area which is to support a construction, it can also be mixed with soil and the resultant mixture pressed into moulds to form building elements for the construction of low cost housing.
According to the present invention there is provided a chemical agent for improving the engineering properties of soil, the agent comprising:
between 5 and 60% by mass of a cementitious pozzalan;
between 20 and 80% by mass of calcium sulphate; and
between 15 and 50% by mass of an oxide of calcium.
It is preferred that the chemical agent for improving the engineering properties of soil comprise:
between 15 and 35% by mass of a cementitious pozzalan;
between 40 and 60% by mass of calcium sulphate; and
between 20 and 40% by mass of an oxide of calcium.
In a still further preferred form the chemical agent comprises:
between 25 and 30% by mass of a cementitious pozzalan;
between 30 and 40% by mass of calcium sulphate; and
between 25 and 35% by mass of an oxide of calcium.
The preferred pozzalan is blast furnace slag mixed with ordinary Portland cement, preferably in equal masses. Blast furnace slag is generally referred to as slagment.
The chemical agent can also includes additional pozzalans selected from ordinary Portland cement (referred to in the industry as OPC), sulphate-resisting cement, Portland cement 15 SL, Portland cement 15 FA, blends of ordinary Portland cement and fly ash, and masonry cement.
The chemical agent can include reinforcing fibres such as fibres of a synthetic plastics material. Preferred fibres are monofilaments of polypropylene.
Between 1 kilogram and 10 kilograms of fibres can be added to each 100 kilograms of chemical agent.
The oxide of calcium can be in the form of calcium oxide (CaO) or calcium hydroxide (Ca(OH)2). The calcium sulphate can be mineral gypsum or partially dehydrated gypsum (CaSO4.1/2 H2O)
In one form the chemical agent includes 1 to 30% by mass of silica oxide (SiO2).
A specific form of chemical agent which is particularly suitable for use in improving the properties of a road surface comprises:
According to a further aspect of the present invention there is provided a method of improving the engineering properties of soil which comprises scarifying the soil to break up and pulverize the soil, applying the chemical agent described above over the soil, mixing the soil and chemical agent, and thereafter compacting the soil.
According to a still further aspect of the present invention there is provided a method of manufacturing building blocks from soil which comprises breaking up the soil, mixing it with the chemical agent, compacting the mixed soil and chemical agent into a mould, and allowing the mixed soil and chemical agent to set and harden.